Blower Output at Constant 3.3V


 

Jason Shaw

New member
I plan on wiring a heater meter up to the stock mechanical relay on a Masterbuilt Electric Smoker.

I need it to output about 3.3V to turn the relay on and off (instead of controlling the blower fan).

If I were to set the min and max fan speed to 28-30%, would it consistently put out a ~3.3V signal?

Would it work in and on/off manner that way?

Otherwise I'll just modify the code to use another pin and 5V with a 1k resistor...
 
Yes, but if you want it to control a relay, you need to set the HM to pulse mode with fan set to min 100, max 100
 
The variable voltage output is 5V-12.1V so it never goes down to 3.3V, and it scales linearly not ON-OFF. As Steve said you can use pulse mode with a MIN of 100% so it turns on and off with 10 second period with the duty cycle equal to the percent output. That's not really great for driving a relay though, because it is going to turn on and off every 10 seconds unless running at 0% or 100%. HeaterMeter doesn't have a bang-bang mode like a thermostat (turning on when the temp drops below the setpoint by a certain hysteresis then turning back on when it passes the setpoint again).
 
Thanks Bryan.

I read about people using it quite successfully in electric smoker forums and sous vide threads... so your baby continues to grow into more than it was intended for lol.

Every 10 seconds might be too much for the mechanical relay in my smoker... and if so I'll probably just get a solid state relay.

I think I probably will just add another voltage regulator hooked up to one of the unused pins on the rj-45 port.
 
Bryan,

I know you must be a busy guy...

But could you tell me more about how the duty cycle is related to the percent output?

Is it always going to signal the relay on/off on a 10 second interval?
 
Bryan,

I know you must be a busy guy...

But could you tell me more about how the duty cycle is related to the percent output?

Is it always going to signal the relay on/off on a 10 second interval?

The 10 seconds is fixed. It's PID output divided by 10. So at 20% PID output, the relay is signaled on for 2 seconds and off for 8 seconds.
 
Last edited:
Confirming what Steve has said. It is compiled in that it is 10 seconds. The time can be extended by changing LONG_PWM_PERIOD in grillpid.c and recompiling, though I've never tried it for anything but 10000 so there may be overflow in some of the calculations if the value is raised beyond a certain point.
 
I ended up running a jumper wire from the output of the microcontroller pin 5 to an unused RJ45 pin that controls the relay on my electric smoker.

I decided I wanted to run the heater meter off the 5V that is built into my electric smoker.

I powering the HM off 5 volts supplied through the RJ45 port. Without 12V power the Piezo buzzer and the blower fan output (which I don't need) don't work but everything seems to be running fine (pi zero w is not a power hog thank goodness).

Do you foresee any problem powering the heater meter off of the RJ 45 port?
 
Should be fine. The +5v pin on the RJ45 jack comes directly off the 5v regulator, which is also connected to the RasPi +5 pins.

For reduced power consumption you can lower the LCD display brightness via the web config.
 
Nope, the traces to the 5V jack there should be big enough to prevent too much drop on the lines, and I power test devices through straight power to the 5V line for weeks at a time with no issues.
 
It ran all day long, and kept the temperature in my smoker pretty close to where I want it. I had some big overshoots with temperature increases, but it settled back down nicely.

Like you said, it wasn't really made with the intention of running an electric relay, but it seems to be working great. With some PID tuning, I think I will be able to eliminate some of the overshoots.

Thanks for this awesome project!
 

 

Back
Top